Technically, they could do that now already. It would just be a single “Meta app” available in all stores, which has in-app purchases for extra features, such as FB, Insta, WhatsApp, Oculus, etc.
They didn’t do it in the last 5 years, so there isn’t really a reason to think that sidloading is the one thing that is preventing them from doing it now.
An adult tells a child to stay off the table because the child does not have the skills to remain safe on its own.
As an adult, I have actually stood on my table to change light bulbs. I know what the table can handle, how to fall, and the risks involved.
Interestingly, iphones have a setting that allows parents to restrict access for their children.
I do not want Apple dictating how I can use my property, since I am an adult and I know what I am doing. Perhaps adults should limit how children install apps. And administrators can likewise limit how users install apps.
Apple sold me the phone, and it’s now my iphone. I want it to be serviceable and usable after Apple ends support. This requires it to function after they block it from accessing the app store. This requires sideloading.